A differential is a component of an axle assembly that is used to transfer torque from a driveshaft to a pair of output shafts (e.g., axle shafts). The driveshaft can be part of a drivetrain powered by a prime mover (e.g., an engine, a motor, etc.). The driveshaft can drive the differential through the use of a drive gear that meshes with an outer gear mounted at the outside of a housing of the differential. In vehicular applications, the differential allows the wheels (e.g., tires) mounted at opposite ends of an axle assembly to rotate at different speeds. This is important when a vehicle is turning because the outer wheel travels over an arc of greater distance than the inner wheel. Thus, the outer wheel must rotate at a faster speed than the inner wheel to compensate for the greater distance of travel. The differential includes a torque transfer arrangement that allows torque to be transferred from the driveshaft to axle shafts of the axle assembly while concurrently allowing the axle shafts to rotate at different speeds as needed. Two example types of differentials include bevel-style differentials and so called “gearless” differentials.
Bevel-style differentials include a differential case that is rotated about an axis of rotation by a driveshaft. The driveshaft can be powered by a prime mover of a vehicle. A gear interface can be used to transfer torque from the driveshaft to the differential case. First and second side bevel gears are mounted within the differential case. The first and second bevel gears are coaxially aligned along the axis of rotation of the differential case and are coupled to axle shafts of an axle assembly. The axle shafts extend through co-axially aligned openings defined by the differential case that are aligned with the axis of rotation of the differential case. An array of pinion bevel gears is mounted within the differential case between the first and second side bevel gears. The pinion bevel gears are rotatably mounted on gear shafts carried with the differential case. The array of pinion bevel gears intermesh with the first and second side bevel gears to form a torque transfer arrangement configured for transferring torque between the pinion bevel gears and the first and second side gears and for allowing the first and second side bevel gears and their corresponding axle shafts to rotate at different rotational speeds with respect to one another.
Similar to a bevel-style differential, a gearless differential includes a differential case that is rotated about an axis of rotation by a driveshaft. A gear interface can be used to transfer torque from the driveshaft to the differential case. The differential case defines co-axially aligned openings aligned along the axis of rotation of the differential case. The co-axially aligned openings receive axle shafts of an axle assembly. Unlike a bevel-style differential, a gearless differential does not include intermeshing gears within the differential case for differentially transferring torque from the differential case to the axle shafts. Instead, gearless differentials include clutches within the differential case for serving this purpose. During normal straight driving conditions, the clutches are engaged (i.e., actuated) such that torque is transferred from the differential case to both axle shafts. During a turn, the clutch corresponding to the outside wheel disengages to allow the outside wheel to rotate faster than the inside wheel. Examples of gearless differentials of the type described above are disclosed by U.S. Pat. Nos. 4,498,355; 5,413,015; 5,715,733; 5,727,430; 6,688,194; 7,874,954; and 8,146,458.